About

The Instituto de Ciencia de Materiales de Madrid (ICMM) is an institute of the Consejo Superior de Investigaciones Cientificas (CSIC) (Spanish National Research Council) founded in December 1986, that belongs to the Area of Science and Technology of Materials, one of the eight Areas in which the CSIC divides its research activities.

Our mission is to create new fundamental and applied knowledge in materials of high technological impact, their processing and their transfer to the productive sectors at local, national and European scales (the true value of materials is in their use), the training of new professionals, and the dissemination of the scientific knowledge.

Erick Castellón, Marcos Zayat and David Levy

The article describes a new concept of an optical hybrid thin-film material that exhibits reversible humidity-driven light transmittance (scattering) properties. The film consists of a dispersive porous structure, with embedded hygroscopic and deliquescent compounds, that is able to scavenge water molecules from humid air to fill up the pores and become transparent to the incident light. Upon exposure to dry air, water is released from the structure and the material recovers its original light scattering properties. The developed thin films can change their transparency when exposed to air with different relative humidity (RH), adjusting the light throughput. This material can, therefore, be used to design new optical switching systems, having the advantage that they do not require liquid crystal, transparent conductive glass substrates, or complex layer-by-layer architectures for operation. In this work, a thin film was prepared by the sol–gel technique using calcium chloride as deliquescent substance embedded in a hybrid silica–titania matrix. At dry air, the thin films show a highly dispersive state, with a light transmittance T = 0.06, while at 51% RH the film exhibits a transparent state with a transmittance T =0.67 (measured at 633 nm).

Conceptual working principle of a humidity-driven light transmittance switching material. a) Scheme of the dry/scattering and humid/transmitting states. b) Scheme of the dry and wet pores, representing the different refractive indices n in dry air, and the n matching between matrix and pores in humid air.